In variable magnification/reduction optical systems for use in document copier machines, either a zoom lens or a fixed focused lens can be used. In order to achieve the required magnification/reduction ratio, such a lens must be positioned prior to the copy operation in order to achieve the required reduction or magnification. In addition, the total conjugate length (TCL) must be altered in order to retain focal sharpness at the image plane. In many machines, the TCL adjustment is accomplished by changing the length of the optical path by altering the position of mirrors in that path. In operation, both the lens and TCL adjustments must be accomplished prior to beginning the copy operation. Other parameters must also be adjusted as fully described in U.S. Pat. No. 4,120,578 and 4,209,248 which patents describe continuously variable scanning reduction systems utilizing a mechanical drive.
U.S. Pat. No. 4,287,461 describes a continuously variable scanning reduction system for the optics of a document copier machine in which the mechanical drive of the above-named patents is replaced by a servo system in which the scanning optical components are driven by a scan drive motor separate from the main drive motor. In that system there is no direct mechanical connection between the scan components and the photo-receptive drum.
In all of the above-named patents, the initial optical setup is achieved through an optics positioning motor which positions the lens and other optical components in response to the desired reduction or magnification ratio selected by the machine operator. It is the general object of this invention to provide an optics positioning system which eliminates the need for a special optics positioning motor.